August 3, 2013

Researchers Work To Create New Ultraslippery Glass Coating

According to a new report in Nature Communications, a team of engineers at Harvard University has developed a revolutionary coating for glass that is self-cleaning, extremely durable and highly slippery.

The researchers said their groundbreaking material could be used on everything from eyeglasses to medical devices and is an improvement on a previously developed coating called Slippery Liquid-Infused Porous Surfaces, or SLIPS. The new coating is just as slippery, more durable and fully transparent.

SLIPS was the slipperiest synthetic surface ever known and was originally inspired by the carnivorous pitcher plant that naturally produces a material on its leaves that causes insects to slide down into the plant to where they are digested. The original SLIPS was also able to effectively repel oil and sticky substances like honey.

Nicolas Vogel, a postdoctoral fellow in applied physics at Harvard who worked on both materials, said SLIPS provided the necessary "proof of principle" step toward creating commercially viable technology.

"SLIPS repels both oily and aqueous liquids but it's expensive to make and not transparent," Vogel said.

The Harvard physicist added that attaching SLIPS to any surface is a difficult undertaking.

"It would be easier to take the existing surface and treat it in a certain way to make it slippery," he said.

To create the new coating, the Harvard team first took small spherical particles of polystyrene, commonly used in Styrofoam, and placed them on a flat glass surface. They then poured liquid glass over the surface until the polystyrene spheres were covered more than half-way. After the glass cooled, the team burned away the beads - which essentially created a honeycomb-like lattice. This porous coating was then covered with the same liquid lubricant used in SLIPS.

"The honeycomb structure is what confers the mechanical stability to the new coating," said lead investigator Joanna Aizenberg, a professor of chemistry and chemical biology at Harvard.

The scientists were able to adjust the size of the honeycomb cells to smaller than the wavelength of visible light, making the coating completely transparent. Besides repelling a wide range of liquids, the new SLIPS material has proven to be extraordinarily robust, resisting damage and remaining slippery.

Another advantage of the new material is that it prevents the adhesion of ice by 99 percent. This frost resistance could eventually be used on power lines, airplane wings and cooling systems.

"We set ourselves a challenging goal: to design a versatile coating that's as good as SLIPS but much easier to apply, transparent, and much tougher - and that is what we managed," Aizenberg said.

The Harvard team said they are planning to refine their method for optimal use on curved pieces of glass and clear plastics. They also plan to adapt their process for manufacturing purposes.

"Joanna's new SLIPS coating reveals the power of following Nature's lead in developing new technologies," said Dr. Don Ingber, the founding director at Harvard's Wyss Institute for Biologically Inspired Engineering at Harvard. "We are excited about the range of applications that could use this innovative coating."